There has been conventionally known image sensors that are close-touching-type photoelectric conversion apparatuses in which large numbers of photoelectric conversion means (e.g. photodiodes, phototransistors) and switching elements (e.g. thin film transistors) are disposed in a line or two dimensionally in lines.
Examples of such image sensors are active-matrix-type image reading apparatuses disclosed in Japanese Publication for unexamined Utility model, No. 2-8055/1990 (Jitsukaihei; publication date: Jan. 18, 1990) and in Japanese Publication for Unexamined Patent Application, No. 5-243547/1993 (Tokukaihei; publication date: Sep. 21, 1993).
As shown in FIG. 14, in the active-matrix-type image reading apparatus, each pixel 81 of active matrix array, in which pixels are arrayed in an X-Y matrix, has an optical-sensor-use TFT (Thin Film Transistor) 82 and a switching-use TFT 83. The optical-sensor-use TFT 82 is a photoelectric conversion element, and the switching-use TFT 83 is a switching element. The optical-sensor-use TFT 82 of each pixel 81 is so designed that electric properties thereof are changed in accordance with whether a photogenic subject, such as a surface of a document, is white or black (bright or dark).
Specifically, because a resistance value of a phototransistor, which is used as the optical-sensor-use TFT 82, is changed in accordance with brightness (bright or dark) of light, an amount of electrical charge in an image capacitor (charge capacitor) connected to the phototransistor, or a voltage applied to each pixel 81 is changed. Therefore, two-dimensional information of the photogenic subject can be obtained by sequentially reading out an electrical charge distribution or a voltage distribution of the image capacitor by using the switching-use TFT 83.
For example, as disclosed in Japanese Publication for Unexamined Patent Application, No. 6-350070/1994 (Tokukaihei; publication date: Dec. 22, 1994), in a close-touching-type photoelectric conversion apparatus, it is necessary, regardless of whether a close-touching-type photoelectric conversion apparatus is one-dimensional line-sensor-use photoelectric conversion apparatus or two-dimensional area-sensor-use photoelectric conversion apparatus, to form a transparent protective layer over photoelectric conversion means, such as thin film phototransistors, photodiodes, or photoconductors, after the photoelectric conversion means is formed on a substrate.
The protective layer is provided for protecting the photoelectric conversion means including semiconductor elements.
Specifically, as shown in FIG. 15, a photoelectric conversion element formation substrate 92, on which photoelectric conversion elements 91 are provided, and a protective layer 93 made of a thin glass substrate, such as a micro glass sheet, are bonded together by using an adhesive resin 94.
In this case, a light source 95, which functions as a backlight, is positioned under the photoelectric conversion element formation substrate 92, on which the photoelectric conversion elements 91 are provided. A document to be read is placed on the protective layer 93. Light emitted from the light source 95 passes through an opening section (transparent section) of the photoelectric conversion apparatus, and is radiated onto the document. The light radiated onto the document is reflected by a surface of the document, and enters into the photoelectric conversion elements 91.
However, the conventional photoelectric conversion apparatuses and manufacturing methods of same have the following problems.
(1) In a case where a high-definition photoelectric conversion apparatus is needed, a thickness of the protective layer (micro glass sheet) must be reduced. For example, in a case of a photoelectric conversion apparatus having a pixel density of 300 dpi, a pixel pitch is approximately 85 μm. In this case, it is necessary to set the thickness of the protective layer to approximately 50 μm, which is thinner than the pixel pitch. Otherwise, inter-pixel crosstalk of the light reflected by the document becomes so significant as to blur an image. In a case where the pixel density is 500 dpi, the pixel pitch is approximately 50 μm. In this case, the thickness of the protective layer must be reduced further, to approximately 30 μm.
If the thin protective layer is made of micro glass sheet, as in conventional arrangements, it is difficult to evenly bond the protective layer, by using the adhesive resin, to the substrate on which the photoelectric conversion elements have been formed. This is because the micro glass sheet is difficult to handle due to fragileness, and can easily be distorted. Therefore, such an arrangement and manufacturing method of the photoelectric conversion apparatus are needed that do not require a process of bonding the micro glass sheet.
(2) To the substrate on which the photoelectric conversion elements are provided, also provided are large numbers of switching elements and the like disposed in matrix or in a line. Therefore, it is necessary to install, in a peripheral portion (edge portion) of the substrate, a driving LSI (Large Scale Integrated Circuit) for driving the switching elements, a reading LSI for reading electric information obtained from the photoelectric conversion elements, and/or a flexible printed circuit (FPC), for example.
In installing the LSIs in the peripheral portion of the substrate, a COG (Chip On Glass) method or a TCP (Tape Carrier Package) method is employed, for example. In the COG method, an LSI chip is directly installed on a substrate. In the TCP method, an LSI is installed to a tape, and the tape is installed on a substrate. In a case where the LSIs are installed by the COG method or the TCP method, or in a case where the FPC (Flexible Printed Circuit) is installed, it is necessary to provide a cover for protecting an installation portion, that is, the portion where the LSIs are installed. As a result, the installation portion in the peripheral portion of the substrate inevitably protrudes toward a surface of the document as compared with the protective layer provided to an image-pickup region.
In a case where close-touching-type photoelectric conversion elements are used, it is necessary to cause the document-to be in close contact with the protective layer, so as to read the image. If the document has a large size, however, the document is hindered from closely touching the protective layer because of the protrusion of the installation portion. This causes problems of distortion and blur in an input image. Therefore, such an arrangement and manufacturing method of the photoelectric conversion apparatus are needed in which the installation portion of the LSIs and the FPC on a document-image-pickup plane, that is, on a surface on which the protective layer is provided, is eliminated.
The present invention is made in light of the problems above. An object of the present invention is to provide a photoelectric conversion apparatus and manufacturing method of same in which (a) the process of bonding the micro glass sheet is not required and (b) the protrusion of the installation portion toward the surface of the document is eliminated.